With the dramatic developments of wireless telecommunication and satellite communication systems, there have been increasing demands for highly integrated RF and microwave circuits with better performance, smaller size and lower cost. Many of these systems use couplers, such as a 3-dB coupler and other directional couplers, in their microwave circuitry. Couplers of many types and variations have been developed for circuits processing signals at microwave frequencies. U.S. Pat. No. 3,516,024 was issued on Jun. 2, 1970 to Lange for an Interdigitated Strip Line Coupler. This coupler, also described in Lange, “Interdigitated Strip-Line Quadrature Hybrid”, MTTS Digest of Technical Papers, Dallas, Tex., May 5-7, 1969, pp. 10-13, has become generally known as a Lange coupler. Since this early work on strip line conductors many variations have been developed.
These are variously described in Waterman, Jr., et al., “GaAs Monolithic Lange and Wilkinson Couplers”, and Brehm et al., “Monolithic GaAs Lange Coupler at X-Band”, both of IEEE Transactions on Electron Devices, Vol. ED-28, No. 2, February 1981, pages 212-216, and pages 217-218, respectively; Tajima et al., “Monolithic Hybrid Quadrature Couplers (Braided Structures)”, IEEE GaAs IC Symposium, 1982, pages 154 and 155; Kumar et al., “Monolithic GaAs Interdigitated Couplers”, IEEE, 1983, pages 359-362; Kemp et al., “Ultra-Wideband Quadrature Coupler”, IEEE Transactions, 1983, pp. 197-199; Shibata et al., “Microstrip Spiral Directional Coupler”, IEEE Transactions, 1981, pp. 680-689; Lentz, “Compact Transmission Line Consisting of Interleaved Conductor Strips and Shield Strips”, U.S. Pat. No. 3,162,717 issued Dec. 22, 1964; Oh, “Three Conductor Coplanar Serpentine-line Directional Coupler”, U.S. Pat. No. 3,332,039 issued Jul. 18, 1967; Presser et al., “High Performance Interdigitated Coupler with Additional Jumper Wire”, U.S. Pat. No. 4,636,754 issued Jan. 13, 1987; and Podell et al., “Spiral Hybrid Coupler”, U.S. Pat. No. 4,800,345 issued Jan. 24, 1989. All of these above cited references are herein incorporated in their entirety by this reference.
These various forms of interdigitated and strip-line conductors provide coupling with various degrees of success for different fabrication technology.